1. Field of the Invention
This invention relates to a method for making porous materials and a method for purifying aqueous phase using such materials. More particularly, this invention relates to a method for making porous, hydrophilic, oxidatively stable materials and a method for purifying hydrophilic compounds using such materials.
2. Background of the Invention
The demand for aqueous-based chemicals continues to increase, partly due to environmental concerns, and partly due to the nonrenewability of petroleum feedstocks. Hydrogen peroxide, alcohols, ethers, carboxylic acids and esters are just a few polar compounds holding promises as green substitutes to more traditional petrochemical-based moieties.
Hydrogen peroxide is a very important chemical, with worldwide production exceeding 2 million tons per year. It is used in advanced and environmentally friendly pulp and paper manufacturing processes, for environmental remediation in other industries, for production of specialty chemicals, for laundry products, for electronics manufacturing, and in many other applications. Demand over the past decade has been growing at an annual rate of 10%.
There is a huge potential for the use of hydrogen peroxide in the manufacture of many large-volume commodity petrochemicals via efficient and environmentally friendly processes. The potential tonnage of chemicals such as propylene oxide, caprolactam, and phenol exceeds 4 million tons per year.
Hydrogen peroxide has the potential of being the ultimate environmentally friendly xe2x80x9cgreenxe2x80x9d chemical. However, current processes for producing hydrogen peroxide are complex. Typical H2O2 production processes are based on anthraquinone reduction chemistry. The process steps are as follows:
(1) hydrogenation of anthraquinone in a fixed bed reactor;
(2) separation of the catalyst fines;
(3) oxidation of the hydrogenated anthraquinone working solution by air in a multi-stage packed bed tower while simultaneously producing H2O2 in the organic stream;
(4) extraction of the H2O2 from the anthraquinone working solution by water in a multistage counter-current extraction column process;
(5) recovery and polish purification of the anthraquinone working solution, the accompanying solvents and their recycle to the hydrogenator; and
(6) recovery, polish purification and stabilization of the H2O2 product. aqueous-based chemicals, such as hydrogen peroxide, are concomitantly generated with less-polar moieties.
The process outlined above, and further disclosed in U.S. Pat. No. 2,158,525 to Pfliderer and U.S. Pat. No. 2,215,883 to Riedel is typical for large scale procedures. Not only do these production processes require multiple steps, but such multi-step procedures require multiple reaction beds, each several feet tall. As such, the incorporation of the above-disclosed processes in small-scale scenarios is not warranted.
U.S. Pat. No. 5,662,878, awarded to the instant Assignee on Sep. 2, 1997, teaches a process for selective pervaporation of hydrogen peroxide (H2O2) through pervaporation membranes to provide an organic free solution. Generally, the pervaporation membranes consist of a nonporous, polyvinyl alcohol active layer on a porous supporting layer. Another membrane, NAFION(copyright) by DuPont, uses a hydrophilic-derivatized Teflon. The ""878 process offers a vastly simplified H2O2 protocol, but still requires multiple steps.
Perfluorinated ionomers, such as the above-mentioned NAFION(copyright), have excellent chemical stability, and because of ionic charge groups, are inherently hydrophilic. NAFION is widely used in commercial chloro-alkali processes and has a long membrane life, despite the rigorous process conditions. However, NAFION and other perfluorinated ionomer membranes, and other ion-exchange membranes are non-porous and thus unsuitable for filtration separation.
Heretofore, the transport mechanisms for any separation applications using membranes were based on either ion exchange (as in the electrochemical applications), or perneation/diffusion (as in the dehydration applications). Such transport mechanisms have several drawbacks, including inherently low flux ( less than 1 kg/m2xc2x7h), the need for very thin (and therefore fragile) membranes, and the need to operate at high temperatures. However, hydrogen peroxide is unstable at high temperatures.
Microporous membranes that are completely coated with perfluorinated ionomers and thus rendered non-porous have been developed by others such as Pellegrino et al, U.S. Pat. No. 5,258,202 and Bardot et al., U.S. Pat. No. 5,342,521. Although such membranes have hydrophilic and oxidatively stable surfaces, the membranes are non-porous and the underlying substrate materials are still subject to oxidative degradation.
A need exists in the art for a method of preparing oxidatively stable, hydrophilic, microporous materials suitable for filtration separation in the presence of hydrogen peroxide or other chemically rigorous environments. The material should be homogenous in that it be made entirely of oxidatively stable materials. A need also exists in the art for a method of separating aqueous phase from organic phase by filtration using such materials.
An object of the present invention is to provide a method for producing hydrophilic, porous materials and a method using the materials for separating chemicals that overcome many of the disadvantages of the prior art.
Another object of the present invention is to provide a method for producing an oxidatively stable material with controlled porosity. A feature of the method is producing gaseous product at catalytic ion-exchange sites of a non-porous, oxidatively stable material to induce regio-specific perforations at those sites in the material. An advantage of this invention is that porosity is controlled by varying the reaction conditions.
An additional object of the present invention is to provide a method for purifying chemicals via pressure filtration. A feature of this invention is utilizing porous hydrophillic membranes to separate aqueous phase from organic liquors. An advantage of the invention is that the method provides a flux of at least approximately 5 kg/m2 hour, and more typically 10 kg/m2 hour which is approximately 10 times higher than the flux achieved by currently-available ion-exchange methods or permeation/diffusion methods. Another advantage is that high through-put of aqueous phase does not decrease significantly as the ratio of aqueous to organic phase decreases.
Still another object of the present invention is to provide a porous hydrophillic material. A feature of the invention is that the material is homogenous in that it is made entirely of oxidatively stable materials. An advantage of the invention is that, unlike microporous structures merely coated with perfluorinated ionomers, the instant material is made entirely of perfluorinated ionomer and thus, is resistant throughout to oxidative degradation.
Briefly, the invention provides for a method for producing a porous, ionic hydrophilic material, the method comprising supplying a nonporous, substrate containing localized ionic hydrophilic chemical clusters; and forming controlled pore sized and evenly distributed apertures in the clusters in situ via chemical reactions.
A method for separating aqueous phases from organic solution is provided comprising supplying an ionomeric membrane having hydrophillic regions defining pores, wherein the membrane has a first surface and a second surface; contacting the organic solution to the first surface for a time and at a pressure sufficient to facilitate transfer of the aqueous phase through the pores; and collecting the aqueous phase from the second surface.
A porous hydrophilic, organic, polymeric material also is provided comprising amorphous ionomeric phases, and regions within said amorphous phases defining apertures.